Can you delete HM's from a a Pokemon's moveset in RBY?
Unfortunately, no as in Generation 1, there is no HM deleter in the game. The first HM deleter found in the games is in Generation 2 in Blackthorn City.
Source: Experience ( I looked all over Kanto in every city route and town with none to be found and also the Gen 2 OFFICIAL strategy guide. ) Sorry tho
No. There is no Move Deleter in Pokémon Red, Blue, and Yellow. You will have to keep HMs in your Pokémon's moveset.
There's actually one way that a friend noticed. If you put a pokémon in the daycare and it learns a new move it forgets the move in the first slot (new move comes in the last slot and everything is pushed upwards) and that works to get rid of HMs.